class Solution {
public:
    int uniquePaths(int m, int n) {
        if (0 == m || 0 == n) { return 0; }
 
        vector<vector<int> > dp(m, vector<int>(n, 0));
        dp[0][0] = 1;
        for (int i = 1; i < m; ++i) { dp[i][0] = 1; }
        for (int j = 1; j < n; ++j) { dp[0][j] = 1; }
        for (int i = 1; i < m; ++i) {
            for (int j = 1; j < n; ++j) {
                dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
            }
        }
 
        return dp[m - 1][n - 1];
    }
};
